1. Field of the Invention
This invention relates to a camera position-correcting method and system for compensating for displacement between the coordinate system of a component-sensing camera and that of a board-sensing camera used e.g. in an electronic component-mounting apparatus, as well as a dummy component for use in correction of camera positions.
2. Prior Art
Conventionally, in an electronic component-mounting apparatus, a board-sensing camera installed therein takes an image of a mark on a circuit board introduced into a main part of the apparatus, thereby sensing a position of the circuit board, while a component-sensing camera also installed in the apparatus takes an image of an electronic component to be mounted on the circuit board, thereby sensing a position of the electronic component. The electronic component is mounted on the circuit board after the position of the component is corrected, based on results of the sensing of the position of the circuit board and that of the component. In this case, however, unless coordinate systems of the two cameras quite agree with each other in both X and Y-directions as well as angle xcex8 (hereinafter, xe2x80x9cxcex8xe2x80x9d is represented as xe2x80x9czxe2x80x9d), the electronic component cannot be mounted accurately on the circuit board even if the correction of the position of the component is carried out.
For this reason, in the conventional electronic component-mounting apparatus, a displacement between the coordinate system of the component-sensing camera and that of the board-sensing camera is compensated for when the apparatus is installed, or periodically (e.g. when the apparatus is in operation) in view of changes in temperature or the like. More specifically, after a real electronic component is mounted on a dummy board introduced into the main part of the apparatus, following the steps described above, the amount of deviation between a design mounting position on the dummy board and an actual mounting position on the same is measured by the use of a measuring device additionally provided, and then a result of the measurement is inputted into the electronic component-mounting apparatus, whereby the displacement between the coordinate system of the component-sensing camera and that of the board-sensing camera is compensated for (displacements of the respective coordinate systems of the two cameras with respect to an absolute reference coordinate system of the apparatus body are also compensated for at the same time).
As described above, in the conventional electronic component-mounting apparatus, the measuring device is needed for correction of the coordinate systems of the two cameras, and at the same time, correction operations including the transfer of the dummy board and the measurement are troublesome and time-consuming. In addition, since a real electronic component is used for the correction, it is required to consider manufacturing tolerances of the electronic component, and hence the mounting and measurement described above is required to be carried out a plurality of times by using a plurality of electronic components, to thereby obtain an average value of the amounts of deviation.
It is a first object of the invention to provide a camera position-correcting method and device which makes it possible to accurately compensate for a displacement between a coordinate system peculiar to a component-sensing camera and a coordinate system peculiar to a board-sensing camera, with ease and rapidity.
It is a second object of the invention to provide a dummy component for use in accurately compensating for a displacement between a coordinate system peculiar to a component-sensing camera and a coordinate system peculiar to a board-sensing camera, with ease and rapidity.
To attain the first object, according to a first aspect of the invention, there is provided a method of correcting a camera position by compensating for a displacement between a first coordinate system peculiar to a board-sensing camera for sensing a position of a circuit board, and a second coordinate system peculiar to a component-sensing camera for sensing a position of an electronic component to be mounted on the circuit board.
This method is characterized by comprising the steps of:
causing the board-sensing camera to take an image of a dummy component in an attitude-fixed state in the first coordinate system;
causing the component-sensing camera to take an image of the dummy component in an attitude-fixed state in the second coordinate system;
calculating an amount of deviation of a center of the dummy component from a sensing center of the board-sensing camera and an amount of deviation of the center of the dummy component from a sensing center of the component-sensing camera, from a result of the taking of the image of the dummy component by the board-sensing camera and a result of the taking of the image of the dummy component by the component-sensing camera; and
correcting at least one of the first coordinate system and the second coordinate system based on the calculated amounts of deviation of the center of the dummy component.
According to this method, in the first place, by taking images of the dummy component by the board-sensing camera and the component-sensing camera in the first and second coordinate systems peculiar to the respective cameras, amounts of deviation of the sensing centers of the cameras from the center of the component sensed in the coordinate systems peculiar to the respective cameras are sensed. The taking of the images is carried out with the dummy component in the respective attitude-fixed states, and hence the two cameras each sense the dummy component in basically identical conditions. As a result, a total sum of deviations of the sensing center of the board-sensing camera and the sensing center of the component-sensing camera from the center of the dummy component form a displacement between the two cameras. Correction of the first coordinate system peculiar to the board-sensing camera and/or the second coordinate system peculiar to the component-sensing camera based on the deviations makes the two coordinate systems agree with each other. That is, the displacement between the two existing coordinate systems caused by the deviations of at least one of the coordinate systems from its or their design coordinate systems can be compensated for through the sensing of the dummy component by the respective cameras. It should be noted that although a real electronic component may be used as the dummy component, the use of a dedicated one made for this purpose is preferred from the viewpoint of accuracy.
To attain the first object, according to a second aspect of the invention, there is provided a camera position-correcting system, comprising:
a dummy component;
a board-sensing camera normally used for taking an image of a circuit board, the board-sensing camera having a first coordinate system peculiar thereto;
a component-sensing camera normally used for taking an image of an electronic component to be mounted on the circuit board, the component-sensing camera having a second coordinate system peculiar thereto;
image-taking operation control means for causing the board-sensing camera to take an image of the dummy component in an attitude-fixed state in the first coordinate system and the component-sensing camera to take an image of the dummy component in an attitude-fixed state in the second coordinate system;
deviation-calculating means for calculating an amount of deviation of a center of the dummy component form a sensing center of the board-sensing camera and an amount of deviation of the center of the dummy component from a sensing center of the component-sensing camera, from a result of the taking of the image of the dummy component by the board-sensing camera and a result of the taking of the image of the dummy component by the component-sensing camera; and
correction means for correcting at least one of the first coordinate system and the second coordinate system based on the calculated amounts of deviation of the center of the dummy component to thereby compensate for a displacement between the first coordinate system and the second coordinate system.
According to this camera position-correcting system, first, the image-taking operation control means controls the board-sensing camera and the component-sensing cameras such that they take images of the dummy component in the first and second coordinate systems peculiar to the respective cameras. Then, amounts of deviation of the sensing centers of the cameras from the center of the component sensed in the coordinate systems peculiar to the respective cameras are recognized or calculated based on the results of the image-taking operations by the deviation-calculating means. The correction means corrects the coordinate systems peculiar to the respective cameras based on the amounts of deviations thus recognized. The taking of the images is carried out with the dummy component in the respective attitude-fixed states, and hence the two cameras each sense the dummy component in basically identical conditions. As a result, a total sum of the amounts of deviations of the sensing center of the board-sensing camera and the sensing center of the component-sensing camera from the center of the dummy component form a displacement between the first and second coordinate systems peculiar to the respective cameras. Correction of the first coordinate system peculiar to the board-sensing camera and/or the second coordinate system peculiar to the component-sensing camera based on the amounts of deviation makes the two coordinate systems agree with each other. That is, the displacement between the two existing coordinate systems caused by the deviations of at least one of the coordinate systems from its or their design coordinate systems can be compensated for through the sensing of the dummy component by the respective cameras.
Preferably, the first coordinate system and the second coordinate system each include an angle of rotation on a horizontal plane.
According to this preferred embodiment, it is possible to compensate for the deviations resulting from errors in mounting angle of the board-sensing camera and the component-sensing cameras within respective horizontal planes, and this makes it possible to mount electronic components on circuit boards with higher accuracy.
Preferably, the camera position-correcting system includes a body, and the component-sensing camera is fixedly arranged in the body based on an absolute reference coordinate system peculiar to the body, and the board-sensing camera is movably arranged in the body based on the absolute reference coordinate system, the camera position-correcting system further comprising a dummy board for being positioned on the body based on the absolute reference coordinate system, and absolute correction means for compensating for a displacement between the first coordinate system and the absolute reference coordinate system, via the dummy board placed on the body, prior to compensating for the displacement between the first coordinate system and the second coordinate system.
According to this preferred embodiment, the absolute correction means is capable of compensating for a displacement of the first coordinate system peculiar to the board-sensing camera with respect to the absolute reference coordinate system by the sensing of the dummy board. Through correction of the first and second coordinate systems peculiar to the respective cameras, the displacements of the two coordinate systems from the absolute reference coordinate system can be compensated for. In other words, the mounting of electronic components on circuit boards can be accurately carried out based on the absolute reference coordinate system.
Preferably, the first coordinate system, the second coordinate system and the absolute reference coordinate system each include an angle of rotation on a horizontal plane.
According to this preferred embodiment, it is possible to compensate for the deviations of the board-sensing camera and the component-sensing cameras with respect to the absolute reference coordinate system, which result from errors in mounting angle of the two cameras within respective horizontal planes.
More preferably, the camera position-correcting system further includes X-Y motion means for moving the board-sending camera in an X-Y direction, and the absolute correction means compensates for the displacement between the first coordinate system and the absolute reference coordinate system, and at the same time compensates for an angular displacement of a moving coordinate system peculiar to the X-Y motion means with respect to the absolute reference coordinate system, via the dummy board placed on the body.
According to the preferred embodiment, an angular displacement between a moving coordinate system peculiar to the X-Y motion means and the absolute reference coordinate system can be compensated for, whereby an error in motion of the board-sensing camera caused by the X-Y motion means can be compensated for.
More preferably, the camera position-correcting system includes a mounting head for mounting the electronic component on the circuit board, and a support member movably mounted on the body, the board-sensing camera, the mounting head, and the support member forming a unit for motion in unison, the mounting head being fixed to the support member based on the absolute reference coordinate system.
According to this preferred embodiment, the mounting head is fixed to the support member based on the absolute reference coordinate system. Therefore, it is possible to mount electronic parts on circuit boards with higher accuracy.
Preferably, the dummy component comprises a transparent base and an imaging pattern depicted on the base.
According to this preferred embodiment, the imaging pattern for being sensed by the cameras is depicted on the base, and hence it has no thickness. The cameras take images of the pattern without thickness, and pattern recognition can be carried out with higher accuracy than when it is carried out on a real electronic component having a thickness. In short, the accuracy of correction or compensation for the displacement or deviations can be enhanced.
Preferably, the camera position-correcting system includes a dummy component-storing device for storing the dummy component therein, and an image-taking table for placing the dummy component thereon to permit the board-sensing camera to take the image of the dummy component, and the image-taking table has a table on which the dummy component is placed, and a backlight for irradiating the dummy component through the table.
According to this preferred embodiment, the dummy component can be equipped for use at all times. Further, by irradiating the dummy component by the backlight when the board-sensing camera takes the image of the dummy component, the pattern recognition can be carried out with higher accuracy. That is, the accuracy of correction of the coordinate systems or compensation for displacement therebetween can be enhanced.
To attain the second object, according to a third aspect of the invention, there is provided a dummy component for camera position correction, which is used for enabling an amount of deviation of a center thereof from a sensing center of a sensing-camera to be sensed through taking an image of the dummy component.
The dummy component is characterized by comprising:
a transparent base; and
an imaging pattern depicted on the transparent base.
According to the dummy component, the imaging pattern for being sensed by the cameras is depicted on the base, and hence it has no thickness. The cameras take images of the pattern without thickness, and pattern recognition can be carried out with higher accuracy than when it is carried out on a real electronic component having a thickness.
Preferably, the imaging pattern is depicted on a lower surface of the base.
According to this preferred embodiment, the imaging pattern can be sensed in the same manner as a real electronic component is sensed by the cameras. This makes it possible to reduce an error in recognition resulting from the difference in image-taking conditions between the an electronic component and the dummy component.
Preferably, the base is formed of glass, and the imaging pattern is formed by vapor-depositing chromium oxide on the base.
According to this preferred embodiment, the imaging pattern having a durability can be accurately depicted on the base made of glass, which makes it possible to sense the accurate pattern with accuracy.
Preferably, the imaging pattern comprises a large number of rectangular pattern elements arranged to generally form a rectangular outline.
According to this preferred embodiment, it is possible not only to recognize the imaging pattern as a whole, and but also to carry out a number of pattern recognitions by using the large number of pattern elements even if the imaging pattern is single. Therefore, by averaging the number of pattern recognition, even higher pattern recognition can be attained.
Preferably, the imaging pattern comprises a plurality of large and small patterns each having an identical center and permitting the sensing of the amount of deviation.
According to this preferred embodiment, when a plurality of cameras which are different in magnification (resolution) are used for pattern recognition, the pattern recognition can be carried out in a manner suitable for the selected resolution.
The above and other objects, features, and advantages of the invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings.